1. Field of the Invention
The invention relates to a centrifugal switch actuator and a motor comprising the same.
2. Description of the Related Art
Centrifugal switches are widely used in many circumstances, especially motors. A motor equipped with a centrifugal switch mainly includes a stator with a primary coil and an auxiliary coil, a rotor, a rotating shaft integrated with the rotor, endshields for supporting the motor body and preventing shock/static electricity, and a centrifugal switch fixed on the rotating shaft. The centrifugal switch is mainly composed of a centrifugal switch body and a centrifugal switch actuator. When the rotor reaches a certain speed, i.e. 70-80% of the startup speed, a centrifugal block of the centrifugal switch body that is mounted on the rotating shaft overcomes the spring resistance to allow a slide plate of the centrifugal switch body to move in the axial or radial direction. The slide plate moves to drive the centrifugal switch actuator to cut off the power supply of the auxiliary coil. The centrifugal switch actuator mainly includes a junction box, a cover, a static contact, a dynamic contact, a reset elastic element, and swing arms, in which the static contact and the dynamic contact are located in the junction box. The swing arms include an outer swing arm outside the junction box and an inner swing arm inside the junction box. The joint between the outer swing arm and the inner swing arm is hinged on the junction box. The inner swing arm is used to push the dynamic contact to open or close the static contact and the dynamic contact while the outer swing arm is used to cooperate with the slide plate of the centrifugal switch body.
The working principle of a motor including the centrifugal switch is as follows: under normal circumstances, the rotor runs at a permissible speed and the slide plate of the centrifugal switch body is against the outer swing arm. When the rotor runs beyond the permissible speed, i.e. 70-80% of the startup speed, the centrifugal block of the centrifugal switch body overcomes the spring resistance to expand outwards to allow the slide plate to move. The outer swing arms then lose the acting force imposed by the slide plate and the reset elastic element enables the swing arms to reset automatically so as to achieve the movement of the dynamic contact under the push of the inner swing arm.
Conventionally, a centrifugal switch actuator has two types of structures: one is that the centrifugal switch actuator, as shown in FIGS. 2 and 3, includes an outer swing arm 205 disposed outside a junction box 201 and two inner swing arms disposed inside the junction box 201, i.e. a first inner swing arm 206 and a second inner swing arm 208. The outer swing arm 205 singly controls both the first inner swing arm 206 and the second inner swing arm 208 simultaneously. The centrifugal switch actuator also includes different length of static and dynamic contact combinations that are parallel with each other in two lines, i.e. a first static and dynamic contact combination 203 and a second static and dynamic contact combination 204. The first static and dynamic contact combination 203 includes a first static contact 2031 and a first dynamic contact 2032 while the second static and dynamic contact combination 204 includes a second static contact 2041 and a second dynamic contact 2042. The first inner swing arm 206 pushes the first dynamic contact 2032 to close or open the first static and dynamic contact combination 203 while the second inner swing arm 208 pushes the second dynamic contact 2042 to close or open the second static and dynamic contact combination 204 so as to finally connect or disconnect the power supply of the motor's auxiliary coil. Since a single outer swing arm is used to control two inner swing arms, the structure of the swing arms is complicated and the requirements for parts machining precision and mounting accuracy are high, or otherwise false operation or malfunction may occur; therefore, the manufacturing costs are high.
Another type of centrifugal switch actuator, as shown in FIGS. 4 and 5, includes two swing arms, i.e. a first swing arm and a second swing arm. The first swing arm includes a first outer swing arm 305 outside the junction box 301 and a first inner swing arm 306 inside the junction box 301 while the second swing arm includes a second outer swing arm 307 outside the junction box 301 and a second inner swing arm 308 inside the junction box 301. The centrifugal switch actuator also includes the same length of static and dynamic contact combinations that are parallel with each other in two rows, i.e. a first static and dynamic contact combination 303 and a second static and dynamic contact combination 304. The first static and dynamic contact combination 303 includes a first static contact 3031 and a first dynamic contact 3032 while the second static and dynamic contact combination 304 includes a second static contact 3041 and a second dynamic contact 3042. The first inner swing arm 306 pushes the first dynamic contact 3032 to close or open the first static and dynamic contact combination 303 so as to finally connect or disconnect the power supply of the motor's auxiliary coil. The second inner swing arm 308 pushes the second dynamic contact 3042 to open or close the second static and dynamic contact combination 304 so as to finally disconnect or connect the power supply of the heating elements. This type of centrifugal switch actuator is likely to produce momentary high current and the safety thereof is poorer than that shown in FIGS. 2 and 3.
The reason why the safety of the centrifugal switch actuator shown in FIGS. 4 and 5 is poorer than that shown in FIGS. 2 and 3 is that the centrifugal switch actuator shown in FIGS. 4 and 5 has the same length of the first and second static and dynamic contact combinations, i.e. the length ratio is 1:1 and the length is relatively short. When the motor runs beyond the permissible speed, i.e. 70-80% of the startup speed, the centrifugal block of the centrifugal switch body overcomes the spring resistance to expand outwards to allow the slide plate to move. The outer swing arms then lose the acting force imposed by the slide plate and the reset elastic element enables the first and second swing arms to reset automatically. The momentary high current is likely to be produced when the first inner swing arm pushes the first dynamic contact to open the first static and dynamic contact combination while the second swing arm pushes the second dynamic contact to close the second static and dynamic contact combination; therefore the motor safety will be affected and the potential safety hazard exists. As shown in FIGS. 2 and 3, the length of the first static and dynamic contact combination 203 of the centrifugal switch actuator is smaller than that of the second static and dynamic contact combination 204, i.e. the length ratios is within the range of 1:1.5-1:2; therefore at the moment when the static and dynamic contact combinations move, i.e. the first static and dynamic contact combination is open while the second static and dynamic contact combination is close, the momentary high current is prevented.